Fluid seal with shaft excursion compensation

Abstract

Compensation for shaft excursion in a seal housing is achieved with a fluid film bearing in which bearing fluid is supplied to the bearing region at a pressure and flow rate which depend upon shaft rotational speed. In a disclosed embodiment, the bearing fluid is provided from a centrifugal fluid seal which delivers part of its fluid to the bearing region as a function of centrifugal pressure. A magnetic fluid seal is employed for zero and low speed operation. The shaft includes an annular collar which rotates in an annular cavity formed in a seal cartridge which is rotationally stationary but capable of small axial displacements to compensate for axial shaft displacement. A spring biases the cartridge in opposition to the axial forces of the magnetic fluid seal so as to axially balance the system at zero and low shaft speed operation. Relative axial motion of the shaft and cartridge occuring at high rotational speeds is balanced by the increasing pressure of fluid delivered to the bearing from the centrifugal seal.